Wrenches having heads that pivot with respect to the wrench's handle axis (“flex-head” wrenches) for adjusting fasteners in hard to reach locations are well known. Existing flex-head wrenches include a fastener-engaging head portion that is attached to a handle at a pivot joint so that a user may adjust the angular position of the head portion relative to the handle. As well, flex-head wrenches may include locking mechanisms for securing the head portion in the desired position relative to the handle during use. Often, these flex-head wrenches are not adequately suited for adjusting the angle of the head portion relative to the handle with only one hand. More specifically, when the locking mechanism is disengaged from the head portion to allow for adjustment, the head portion pivots freely about the handle. As such, a user must grasp the head portion with one hand for positioning while operating the locking mechanism with the remaining hand. Also, in flex-head wrenches that do not have locking mechanisms, it is not uncommon for the head portion to pivot unexpectedly relative to the handle when torque is applied to a fastener.